Why does not promotion engine work stably in Hybris?

As I have observed, Promotion engine (drools-based) has not worked stably in Hybris. For instance, I have a promotion named free-shipment if your order total is more than $150, you will have free shipment.Whenever I deploy the new release of Hybris (v6.4) to production environment, it would not work. When I redeploy the same promotion, it would work.

This has happened in my local environment without no reason as well. Promotions have not frequently worked unexpectedly till redeploying them.(It is possible to say the reason is because of changing current branch but I could not)

Has anybody ever experienced such a situation? What would be the reason?